The present invention relates to an electron gun for a color cathode ray tube and, more particularly, to an electron gun for a color cathode ray tube in which a field emission array cell is employed as an electron emitting source.
A general color cathode ray tube includes a panel 10 on the inner surface of which a fluorescent film (not shown) is located, a funnel 20 sealingly coupled with the panel 10, an electron gun 30 installed in the neck portion 21 of the funnel 20, and a deflection yoke 23 around the cone portion 22.
In the cathode ray tube of the above construction, an electron beam emitted from the electron gun 30 is deflected by the deflection yoke 23, collides with the fluorescent film, and excites a fluorescent material, thus forming a picture.
FIG. 2 shows an example of an electron gun in the neck portion of the funnel for thermionic emission.
The electron gun 30 includes a cathode structure 31 including a field emission array cell having electron emitting portions 31R, 31G, and 31B spaced from each other by a predetermined distance on a substrate 31a for emitting electrons for making red, green, and blue fluorescent materials radiate light, and a focus and a final acceleration electrode 32 and 33 for forming an electron lens for focusing and accelerating the electron beam.
Electron beam transmitting holes 32R, 32G, and 32B and 33R, 33G, and 33B corresponding to the electron emitting portions 31R, 31G, and 31B are respectively formed in the focus electrode 32 and the final acceleration electrode 33.
In the operation of a conventional electron gun for a color cathode ray tube having the described construction, the electron beam is emitted from the electron emitting portions 31R, 31G, and 31B when a predetermined voltage is applied. The emitted electron beam is focused and accelerated by a main lens located between the focus electrode 32 and the final acceleration electrode 33 and lands on fluorescent material of the fluorescent film.
However, the conventional electron gun for a cathode ray tube has the following problems.
First, since the electron beam is emitted from the electron emitting portion including the field emission array cell at an angle of more than 20 degrees, spherical aberration is generated in a main electron lens that is larger than the aberration of an electron gun having a hot cathode in which the incidence angle is less than 5 degrees.
Second, according to the prior art, in order to focus the electron beam emitted from the electron emitting portions 31R, 31G, and 31B into a pixel, an "eccentric distance" S1, which is hereinafter defined as the distance between the electron trasmitting hole or the electron emitting portion positioned in the center of an axial direction of the electron gun and the electron beam transmitting holes or the electron emitting portions positioned on both sides thereof. The electron beam transmitting holes 32R, 32G, and 32B in the facing surfaces of the focus electrode 32 differs from "eccentric distance" S2 between the electron beam transmitting holes 33R, 33G, and 33B in the facing surface of the final acceleration electrode 33. Thus the electron beams on both sides converge on the electron beam of the central portion. At this time, since the above-mentioned convergence is performed in a state in which the electron beam is accelerated, the effect thereof is negligible.
Third, the section of the electron beam landing on the fluorescent film is distorted. Specifically, since the electron emitting portions 31R, 31G, and 31B of the cathode structure 31 are circular, the section of the electron beam focused, accelerated and passing through the main lens becomes circular. The electron beam passes through a non-uniform magnetic field formed by vertical and horizontal deflection coils and the section of the electron beam deflected toward the peripheral portion of the fluorescent film becomes elongated in the horizontal direction. When the elongated electron beam lands on the fluorescent film, a core section and a hazy section are generated in the horizontal direction and the vertical direction, respectively, thus deteriorating the sharpness of the picture.